1. Field of the Invention
The present invention relates to a broadband switching drive compensating circuit for a video display device, and more particularly to a broadband switching drive compensating circuit in a multi-mode video display device having a broadband frequency, capable of performing stable switching operations of a switching power transistor by compensating the drive conditions of the switching power transistor according to horizontal size changes and horizontal frequency changes.
2. Description of the Related Art
In general, a cathode ray tube(CRT) used for a video display device employs a principle of emitting light of different brightness and colors by striking fluorescent materials of red, green, and blue (R, G, B) colors which is coated on the surface of the cathode ray tube with different amounts of electron beams according to the intensity of a video signal. The cathode ray tube (CRT) is widely used since its price and display performance are excellent.
A video display device employing a cathode ray tube inputs a video signal and a synchronous signal from a video card of a computer system and displays information on a screen, which is constituted with a video system for processing a video signal, a deflection system for carrying out vertical and horizontal deflection and a power supply system.
A video card in a host device, such as a computer, supports diverse video modes, and the video modes have different horizontal frequencies and vertical frequencies according to resolutions to be displayed. In particular, if a video card supporting various modes such as VGA, SVGA, a video card supporting a high resolution-dedicated mode, and so on is built in, horizontal frequencies for respective modes are in a range of 30xcx9c75 KHz.
Accordingly, when video modes are changed in a multi-mode video display device, an internal circuit of a video display device has a portion to be modified, for example, in display sizes, position changes, horizontal and vertical synchronization, and deflection system optimization.
In an exemplary multi-mode video display device having a broadband frequency, since the driving conditions of the horizontal output transistor are changed if a horizontal size of a displayed video image is changed or a horizontal frequency is changed, there exists a problem in that the horizontal output transistor carries out unstable switching operations.
The exemplary deflection circuit has a drawback in that built-in components may be damaged by excessive heat generation based on the distorted driving conditions of the horizontal output transistor since many of the values in the circuit are fixed.
Further, an active time of the horizontal output transistor is different in every horizontal frequency, thus the base current of the horizontal output transistor should be changed in order to satisfy the driving conditions of the horizontal output transistor if the horizontal frequency is changed. However, since the base current of the horizontal output transistor is fixed, there again exists a problem in that built-in components may be damaged by excessive heat generation based on the distorted driving conditions of the horizontal output transistor.
In order to solve the above problems, it is an object of the present invention to provide, in a multi-mode video display device having a broadband frequency, a broadband switching drive compensating circuit for a video display device capable of compensating the drive conditions of a switching power transistor according to the changes of the horizontal size and horizontal frequency.
In order to achieve the above object, the circuit according to the present invention comprises a horizontal size detecting unit for detecting a horizontal size of a displayed video image; a horizontal frequency detecting unit for detecting a horizontal frequency; a first DC (direct current) voltage generating unit for generating a first DC voltage according to the detected horizontal size; a second DC voltage generating unit for generating a second DC voltage according to the detected horizontal frequency; a driving current compensating unit for altering a B+1 driving current according to the generated first and second DC voltages; and a horizontal deflection unit for switching a horizontal output transistor according to the altered B+1 driving current and then supplying a sawtooth current to a horizontal deflection coil.
Accordingly, in a multi-mode video display device having a broadband frequency, the driving conditions of a switching power transistor is compensated according to the changes of the horizontal size and the horizontal frequency for establishing the driving conditions of the switching power transistor to the optimum conditions, to thereby perform the stable switching operations of the switching power transistor.